In real time communication, for example, but not limited to, in a collaboration product, delay may be the key to the competitiveness of a product. The delay typically includes the time difference between capturing/encoding of a video frame at a sender and receiving/decoding of the video frame at a receiver. Minimization of the delay can add critical business value to collaboration, or other real-time communication, products.
In a client-server system for multipoint communication, the delay is mainly the sum of uplink delay and downlink delay, which represents the time for sending the frame from a sender to a server, and the time for sending the frame from the server to a receiver, respectively, as given the limitation of available bandwidth, the time used for encoding and decoding is generally negligible compared to the transmission time.
Minimizing uplink delay may be achieved by higher encoding efficiency. Practically speaking, rate control may be applied to control the outcome of the encoder to adapt to uplink bandwidth, but typically at the price of quality fluctuation. When a fixed required quality is taken as a premise, coding efficiency is essential.
Minimizing downlink delay typically becomes more complex when downlinks are at different bandwidths in a multi-point system. US Published Patent Application 2013/0166650 of Chen, et al. and a priority-driven switch of U.S. patent application Ser. No. 14/272,821 of Chen, at al., utilize the concept of key-frame layer or priority layer to make the control of the downlink delay possible.